This X-ray image of the hot gas in the Perseus galaxy cluster was made from 16 days of Chandra observations. Researchers then filtered the data in a way that brightened the contrast of edges in order to make subtle details more obvious. An oval highlights the location of an enormous wave found to be rolling through the gas. (Photo : NASA's Goddard Space Flight Center/Stephen Walker et al.)

It started as a relatively harmless event when a small galaxy cluster passed by the Perseus cluster billions of years ago, according to a report from Atlas Obscura. The action of this smaller cluster bumped into Perseus -- one of the most massive known objects in the entire universe -- creating a gigantic wave of hot gas rolling out. This tsunami extends 200 light-years wide, roughly twice the size of the Milky Way galaxy.

Galaxy clusters are the largest gravitational structures in the universe, and the Perseus cluster stretches 11 million light-years across.

"Perseus is one of the most massive nearby clusters and the brightest one in X-rays, so Chandra data provide us with unparalleled detail," lead scientist Stephen Walker at NASA's Goddard Space Flight Center in Greenbelt, Maryland, said in a statement. "The wave we've identified is associated with the flyby of a smaller cluster, which shows that the merger activity that produced these giant structures is still ongoing."

NASA revealed that they were able to detect the wave by combining data from their Chandra X-ray Observatory with radio information and computer simulations.

One particular simulation seemed to explain the concave feature -- dubbed the "bay" -- in Persues cluster's central galaxy NGC 1275. In this simulation, the gas in a cluster resembling Perseus were divided into two components: a central region 54 million degrees Fahreheit (30 million Celsius) and a zone around it where the gas was three times as hot. A smaller cluster grazed this cluster.

This slight bump formed "a gravitational disturbance that churns the gas like cream stirred into coffee, creating an expanding spiral of cold gas." Now, 2.5 billion years later, the gas has risen 500,000 light-years from the center and the waves surge at the periphery for hundreds of millions of years.